The present invention relates generally to the field of metal founding and, more particularly, to an improved method and system for treating and casting metals.
Heretofore, a number of techniques have been proposed for treating cast metals alloys, such as the various ferrous metal alloys. These include sandwich, tundish, flotret (registered trademark), sigmat (registered trademark), and inmold (registered trademark) processes which form the bulk of the processes used in the ductile iron processing. Among all these different processes the inmold process achieves the highest treatment efficiency. In the inmold process, which this invention comes closest to, chemically reactive agents are introduced into a molding assembly prior to pouring of the casting metal so as to treat such metals prior to entering the molding cavities, thereby imparting certain characteristics to the cast metal. For example, in the casting of ferrous metals, the treating chemicals can include magnesium and rare earths.
The present invention relates to an improvement over heretofore known methods, for instance, the inmold process using vertically parted mold cavities for the production of nodular ductile iron castings. Due to several difficulties experienced in the practical utilization of the inmold process on vertically parted molds, different versions of the treatment method have been tried in the past. In all cases the reaction chamber is located directly underneath or close to the pouring cup to facilitate the alloy addition. In the more popular version, for example, chemical reactive agents, such as certain nodularizing alloys containing modifiers, such as calcium and magnesium, are introduced into a separate reaction chamber which is separate from the receiving basin. The reaction chamber is offset with respect to a receiving basin in the initial part of a runner system leading to the molding cavity. In this approach, the treatment operation commences with passing the molten metal through a reaction chamber which chamber has a specific amount of treating material therein, for example magnesium ferrosilicon, in order to react with cast iron. A meltable metal plug is inserted in the bottom of the receiving basin directly over a downsprue leading to the molding cavity. This is done in order to restrain flow to the molding cavity for a time sufficient to alloy the treating material with the molten metal to be cast. Until the metal plug melts, the poured metal is retained in the basin for a preselected period of time so that the reaction products and other inclusions travel to the surface of the metal. After the plug melts, the treated molten metal enters the casting cavities.
While there are advantages to this approach, there are, however, a number of shortcomings. For example, the pouring rate has to be rigorously controlled in order to insure that the treating chemical reagents generally uniformly react with the molten metal in a controlled manner before entering the treating basin. However in practice, effecting this control is often relatively difficult to achieve and relatively complicated gating systems are used. Moreover, this approach tends to limit the usable mold space for castings and, therefore, the metal yield per mold due to the reaction chamber being located separately from the basin. In addition, the treatment of the metal is not as homogeneous as it could otherwise be. There is also a certain loss of metal temperatures due to the greater volume of the gating system.
While such techniques have overall provided improvements in casting processes, there is nevertheless a continuing desire to improve upon them.